U.S. Pat. No. 4,163,661 discloses grass herbicides which are alkyl esters of 4-methyl-4-[4'-(4"-trifluoromethyl-phenoxy)-phenoxy]-crotonic acid.
U.S. Pat. No. 4,134,753 discloses herbicidal 4-halo-4'-nitro-3'-alkanoyloxy-diphenyl ethers.
U.S. Pat. No. 4,093,446 discloses herbicidal 4-trifluoromethyl-4'-nitro-diphenyl ethers.